Classic potentiometers consist of an ohmic resistance element formed of a coiled wire or of an extended resistance wire or of a resistance path. The element has two electric connections at the exterior and therebetween a movable sliding contact forms a tapping electrode. The sliding contact is activated either via a sliding device or via a rotary device. If one applies a voltage to the exterior electrodes, the tap divides this voltage according to its position along the resistor path. The divided voltages are proportional to the resistance portions lying between tap and exterior electrodes. The total ohmic resistance thereby always remains the same. Such classic potentiometers have the disadvantage that the sliding contact becomes noisy and that the life span is delimited by the wear and tear of the contact.
The tap can be designed contactlessly in order to prevent this. Either the sliding contact is replaced by a different contacting, for example, by exposing the desired tap location in a photoconductor rail, which then produces the connection of the point in the resistance element corresponding with the point to be contacted with the tapping electrode, or one alters the resistance value of two partial elements with fixed tap connection by means of exterior influencing, for example, by means of a magnetic field in magnetic field-dependent resistance elements.
In the first case, the disadvantage exists that the activated portion of the photoconductor layer which produces the contact to the tapping electrode has itself a resistance value. In the second case, a linearity is difficult to produce, in particular when an electronic circuit connected to the subjective divider arrangement is required in order to divide the desired electric magnitude.